Prussian blue

About the chemical structure:

Chemical name:	Iron(III)-hexacyanoferrate(II)
Formula:	Fe[Fe3+Fe2+(CN)6]3
3D model:	orange = iron, yellow = cyanide ion; crystal water: red = oxygen, white = hydrogen
Crystal system:	cubic
Refractive index:	isotropic

Color:

Color Index (C.I.)

PB27

How can you identify Prussian blue?

Imaging:

UVF: no

IRFC: black

Maestro della Maddalena, XIII century, Italy

Left, visible image. Middle, IRFC image. Right, restoration mapping: blue, original XIII century, red XVIII century restoration, blue XIX century restoration.

The blue bonnet of the Virgin shows up in red (left side) and black (right side) in the IRFC. Indeed, the left was restored with indigo in the XVIII century, while the right side was repainted in prussian blue.

OM: Small particles with a greenish hue. Particles clump in amorphous aggregates. Technically the pigment is a ferric ferrocyanide and is so finely divided that it resembles a dye. Soft particles with an average size of 0.5μm.

Microscopic appearance at x500 mag

Analytics:

It's identified by means of FTIR and Raman. Soluble in 10% oxalic acid. Decomposes rapidly on ignition and leaves a residue of ferric oxide.

Raman spectra: University College London;

FTIR spectra: IRUG

Usage and handling:

Permanence:	Toxicity:
Lightfast: very good. Degradation processes: Fairly permanent in light and air.	non toxic. MSDS: Kremer

Literature:

Artists’ Pigments. A Handbook of Their History and Characteristics, Vol. 3: E.W. Fitzhugh (Ed.) Oxford University Press 1997, p. 191 - 217.

Ludi, A. Berliner Blau, Chemie in unserer Zeit, 22, 1988, p. 123

Ludi, A. Prussian blue, an inorganic evergreen, J. Chem. Educ. 58, 1981, p. 1013

Schmidkunz, H. Berliner Blau - ein farbintensives Pigment, Naturwissenschaften im Unterricht-Chemie, 4 , No. 5 (20), 1993, p. 20

Tracey D. Chaplin, Alicia Jurado-Lopez, Robin J. H. Clark, and David R. Beech, Identification by Raman microscopy of pigments on early postage stamps: distinction between original 1847 and 1858–1862, forged and reproduction postage stamps of Mauritius, J. Raman Spectrosc. 2004; 35: 600–604